1. Field of the Invention
The present invention relates to a photographic processing apparatus such as a photographic processing device or photographic printer. In particular, the present invention relates to a photographic processing apparatus having a mirror tunnel for diffusing light from a light source and then leading it onto a film negative. In addition, the present invention relates to a light source device for irradiating light from a light source onto a film negative during a scanning or printing processes.
2. Discussion of the Related Art
Various photo processing apparatuses have been proposed for irradiating light from a light source such as a halogen lamp onto a negative and printing an image of the negative onto a photosensitive material. These photo processing apparatuses are generally provided, for example, with a mirror tunnel 51 shown in FIG. 5 on an optical path between the light source and the film negative. FIG. 5 shows a general structure of a mirror tunnel 51 which is referred to, for example, in Japanese Patent Provisional Publication No. 82869 (1996).
The mirror tunnel 51 comprises a cylindrical mirror tunnel main body 53 having a light reflecting surface 52 formed on the inner surface thereof and diffuser plates 54 and 55, each being disposed on the light incoming side and light outgoing side of the mirror tunnel main body 53 respectively. The diffuser plates 54 and 55 are made of, for example, ground glass or resin such as PMMA (methacrylic resin) and the like containing an opaline pigment.
Due to the structure described above, the light from the light source is diffused by the diffuser plate 54 disposed on the light incoming side of the mirror tunnel 51 as it enters the mirror tunnel 51. Then the incident light is reflected and diffused by the light reflecting surface 52 in the mirror tunnel 51. After having been re-diffused by the diffuser plate 55 disposed on the light outgoing side of the mirror tunnel 51, the light radiates onto the film negative. Even if a point light source such as a halogen lamp and the like is used, the film negative can be substantially uniformly exposed by irradiating the diffused light using the mirror tunnel 51, so that non-uniform exposure between the optical axis and its periphery can be minimized.
Various light source devices have been proposed for irradiating light from a light source onto a film negative during the process of scanning a photo film or of printing it on a photosensitive material such as photographic printing paper. In these light source devices, a halogen lamp is generally employed as a light source.
Light irradiated from a halogen lamp is non-uniform in quantity due to the shape of the filament or an effect of the reflector. On the other hand, the negative film requires uniform light to be irradiated over the entire image area. Therefore, the light source device is inevitably required to be provided with a structure for making the light from the halogen lamp uniform between the halogen lamp and the film negative.
For uniformalizing light (making the light from the halogen lamp uniform), for example, a structure including an optical condenser lens and an optical diffuser means arranged in this order between the halogen lamp and the negative film is employed. According to this structure, the light irradiated from the halogen lamp is condensed by the condenser lens, and the condensed light is diffused by the optical diffuser means. Thereby uniform light is irradiated onto the film negative. As for the optical diffuser means, for example, a mirror tunnel 51 shown in FIG. 5 is used.
Since the diffuser plate 54, as described above, is made of ground glass having opaline materials, the quantity of light is lowered by some one-tenth when light from the light source is transmitted through the diffuser plate 54, and the same degree of drop in the quantity of light also occurs in the diffuser plate 55.
On the other hand, when the light source having the structure described above is used, for example, in a scanner, the light irradiated onto a negative film is detected by a CCD (Charge-Coupled Device). The CCD provides an image with wider contrast when the quantity of light received from the image is widely dispersed within a range of the uppermost and the lowermost limits of a sensor of the quantity of light. This means that the light irradiating the negative film is required to have a certain quantity of light.
Therefore, in the structure of the conventional photo processing apparatus, the power of the halogen lamp is increased in order to compensate for decreased quantity of light which occurs when the light from the light source passes through two diffuser plates 54, 55. As a result, there are problems with increased power consumption of the halogen lamp and an increased cost of the halogen lamp.
At the same time, there is also a problem of an increased quantity of heat discharged from the halogen lamp due to the increased power of the halogen lamp. This requires a cooling device, for example, a fan for cooling the inside of the light source resulting in an additional increase in power consumption.
Since non-uniformity in illuminance on the film negative increases when the power of the halogen lamp is increased, light diffusion by the light diffuser means has to be further enhanced. For example, in the case described above, the diffuser plates 54, 55 of the mirror tunnel 51 may be thickened to enhance the diffusion effect in the mirror tunnel 51. However, the thicker diffuser plates 54, 55 make the quantity of light lower, and this requires a higher capacity light source.
As an alternative method for preventing non-uniformity in the illuminance on the negative film, the mirror tunnel 51 may be formed longer along an optical axis to increase reflection times in the mirror tunnel 51 and thereby enhance the diffusion effect. However, this method makes the mirror tunnel 51 larger and therefore causes a problem due to the larger size requirement for the light source device itself.